This disclosure relates generally to rotary earth-boring drill bits. More particularly, this disclosure relates to a combination drill bit that includes an inner gauge ring that stabilizes the drill bit.
Rotary drill bits are typically mounted on the lower end of a drill string that is being rotated from the surface or by downhole motors. As the drill string is rotated, tension is applied to the drill string to control the weight on the bit so that the bit engages and drills a borehole into the earthen formation.
Two types of available drill bits are roller cone bits and fixed cutter bits. Roller cone bits often include a plurality of conical rollers that rotatably mounted to the bit and imbedded with a plurality of cutting elements. Fixed cutter bits rely on a plurality of fixed blades angularly spaced about the bit and imbedded with a plurality of cutting elements. The cutting elements for either bit design are often formed from extremely hard materials such as polycrystalline diamond material, cubic boron nitride, and tungsten carbide. The configuration or layout of the rollers, blades, and cutter elements vary widely between bit designs depending heavily on the formation to be drilled.
While the bit is rotated, drilling fluid is pumped through the drill string and directed out of the face of the drill bit through one or more nozzles. The drilling fluid acts to cool the bit and remove formation cuttings from the bit face and the bottom of the borehole. During the drilling of a borehole, the drill bit will occasionally become worn out and have to be replaced. Each time the bit is replaced, the entire drill string, which may be thousands of feet long, must be retrieved from the borehole and then reinserted once a new bit has been installed. This process, known as a “trip,” can take many hours to complete. Therefore, it is desirable to employ drill bits which can drill longer distances before needing to be replaced.
The length of time that a drill bit may be used before it must be changed is highly dependent on wear and/or damage to the cutting elements of the drill bit. One of the factors that can cause excessive wear and damage to cutting elements is bit instability. Bit instability can create vibrations that result in impact loads on the cutting elements, which can cause excessive wear or even break cutting elements. Improving bit stability can reduce the likelihood of the high impact loads and improve the life of a drill bit.
Thus, there is a continuing need in the art for rotary drill bits that provide enhanced stability so as to overcome these and other limitations of the prior art.